The invention relates to pump systems in general, and more particularly to improvements in pump systems which can be used to inject fuel into the combustion chambers of internal combustion engines, such as diesel engines.
The pump system which is used to inject fuel into the combustion chamber of an internal combustion engine, such as a spontaneous-combustion engine, normally comprises a pump element which forces fuel to flow from a source into an injector nozzle by way of a delivery or relief valve which is connected with the holder of the nozzle by a high-pressure conduit.
It was already proposed to provide the pump system which serves to supply fuel to the combustion chamber or chambers of an engine with means for admitting several different fuels, either simultaneously or in a selected sequence. Prior proposals include mixing two or more different fuels, admission of fuels to promote ignition and combustion, admission of different fuels during different stages of operation of the engine, and utilization of a first fuel while the engine is hot in order to prepare for injection of a different second fuel whose viscosity, combustibility and/or other characteristics are less satisfactory than those of the first fuel.
In accordance with a presently known proposal, the engine is provided with several injection nozzles for each combustion chamber and each of several nozzles can receive a particular type of fuel. Reference may be had to German Offenlegungsschrift No. 32 21 374. A drawback of such proposal is that additional nozzles contribute to the bulk of the engine and to complexity of the pump system.
German Offenlegungsschrift No. 30 12 418 proposes to provide the nozzle with several inlets each of which extends to the tip of the nozzle to supply a particular type of fuel. The proposal is not entirely satisfactory because it renders it necessary to greatly enlarge the dimensions of the nozzle so that the nozzle can provide separate paths for the flow of different fuels to the outlet opening.
In accordance with a further proposal which is described in German Offenlegungsschrift No. 29 22 682, several types of fuel are supplied through bores in the pin or pintle of the injection nozzle. This proposal has failed to gain acceptance because the dimensions of the pintle [and hence of the entire injection nozzle) must be unduly increased in order to provide sufficiently large paths for the flow of several fuels while at the same time ensuring that the pintle will stand the pressures which develop in the injector nozzle.
All of the above discussed proposals involve the utilization of additional nozzles or substantial modifications of existing nozzles. Further proposals include the provision of plenum chambers in a manner as described in German Offenlegungsschrift No. 29 24 128, storage chambers with valves as described in German Pat. No. 568,366, and even the provision of additional delivery or pressure relief valves as disclosed in German Offenlegungsschrift No. 31 17 796. German Pat. No. 29 32 325 proposes to mix several fuels in the main pump element and to convey the resulting mixture to the injector nozzle.